1. Field of the Invention
The invention relates to a multi-layer damping foil or anti-drumming foil.
2. Description of Related Technology
Damping foils or anti-drumming foils are employed, in particular in the automobile industry, for the sound deadening, i.e. sound damping, of sheets or panels. In particular, such damping foils can be placed in the interior roof and side regions of a body and there adhere firmly all over the surface. Frequently, such damping foils are painted over. The all-over surface adherence is attained, in accordance with the state of the art, in that the side of the damping foil towards the sheet or panel to be damped is provided with a hot-melt glue and after application of the damping foil onto the sheet to be damped a heat treatment is carried out which brings about the melting of the hot-melt glue and therewith attains the all-over surface gluing. In order to be able to hold the damping foil in position before the heat treatment, in particular in the case of roof and side regions of a body, in accordance with the state of the art such a damping foil is constituted to be magnetisable. For this purpose, previously, rod or strip-shaped metal parts have been set into the side of the damping foil towards the sheet to be damped (DE 38 25 494 A1) or there are mixed into the damping foil, in its production, ferrite powder or similar magnetic or magnetisable powdery particles (DE 34 27 916 A1). Damping foils constituted in this way adhere during the heat treatment to the body sheeting due to their own magnetic properties, or due to permanent magnets arranged on the outer side of the sheeting, which attract the magnetisable particles in the damping foil and therewith the entire damping foil. After it had been determined that it was sufficient to correspondingly constitute only a certain layer thickness, it was proposed to employ a multi-layer structure with which a lower layer, towards the sheet or panel, contains magnetic or magnetisable particles and that a layer away from the sheet or panel, which layer fulfils in substance the damping function, does not need such particles. Between these layers, both in general including bituminous material, there can be embedded, in accordance with the state of the art, a flexible foil of aluminium or polyethylene (EP 0 285 740 B1).
In particular the layer towards the sheet to be damped, having the magnetic or magnetisable particles, has high mass per unit area and thus determines the overall weight of the damping foil to be applied to a very significant degree, without this layer contributing significantly to the damping.